1. Field of the Invention
The present invention relates to a method of manufacturing a photoelectric transducer, more specifically relates to a method of manufacturing a photoelectric transducer which comprises a metal film as, light-reflecting layer on a conductive substrate and, semiconductor thereon comprising a non-monocrystalline material containing silicon atoms as the matrix. In particular, it relates to a method of manufacturing a photoelectric transducer that forms a photovoltaic device in a high yield, and that is uniform and durable for long period use.
2. Related Background Art
Conventionally solar cells, which are photoelectric transducers converting sunlight into electric energy, have been widely used as small power sources for pocket calculators and watches and other consumer goods and are expected to provide future practical technology for a future electric power source that replaces so-called fossil fuels sources.
Such solar cells are based on a technology using the photovoltaic effect of a pn junction and others in the functional parts. Semiconductor materials which constitute the pn junction generally are silicon and germanium. Such semiconductors like silicon absorb sunlight and generate electron and hole photo-carriers, which are caused to drift by the internal electric field of the pn junction to the outside.
While a monocrystal is desirable from the standpoint of efficiency in converting light energy to electromotive force, a crystalline silicon in monocrystalline form has indirect optical ends and its absorption of light is small; thus, it has disadvantages in that a solar cell of monocrystalline silicon has to be of at least 50 microns in thickness for absorbing incident sunlight and in that short wave components are not effectively used because the band gap is about 1.1 eV which is narrower than the 1.5 eV suitable for a solar cell.
Even if a polycrystalline silicon is used for lowering the production cost, the thickness of the solar cell cannot be decreased because the problem of indirect optical ends remains unsolved. Furthermore, a polycrystalline silicon also has other problems like grain boundary. It is generally recognized that a fine crystalline silicon and an amorphous silicon derived material are advantageous which are non-monocrystalline and formed by a chemical vapor deposition (CVD) method for the purpose of making the area large and lowering the cost. While amorphous silicon solar cells, which are made of non-monocrystalline semiconductors and are able to be made into thin films, have been prevalent as small power sources for consumer goods, problems in efficiency and stabilization have to be overcome for their use as electric power cells.
The inventors have studied non-monocrystalline silicon solar cells formed on a conductive substrate and recognized the importance of the conductive substrate and the interface conditions of the metal layer and others formed thereon. Thereby, the inventors have found that poor adherence, the existence of impurity, and a poor junction lower the conversion efficiency of the solar cell and bring deterioration of the reliability, durability and production yield. This means the cleaning method of the conductive substrate is very important, however, the conventional cleaning method of the substrate has been tried to be improved only by the use of a solvent or washing with water.
Such conventional methods of substrate cleaning, however, will not result a satisfactory cleaning effect; in particular, the problem, in the area where many layers of various thin films are laminated on a conductive substrate, is the difficulty of satisfying the characteristics of the photoelectric transducer while providing uniform film quality and attaining stable and constant production in a high yield of high quality deposited films durable for long period use.
The photoelectric transducer, manufactured by a method that comprises forming, on a conductive substrate, a metal layer as a light-reflecting layer, a reflection enhancing layer thereon, and a semiconductor photovolatic layer comprising a non-monocrystalline material containing silicon atom as the matrix by a plasma CVD method, has layers of relatively thin films; its manufacturing method comprises many steps where the temperature is relatively high. Therefore, the adhesion between the conductive substrate and the metal layer formed thereon, the presence of impurities, and the conditions of the junction are very important for improving the conversion efficiency of the photoelectric transducer, its reliability, and the manufacturing yield.
It is therefore strongly desired to develop a method of manufacturing a photoelectric transducer comprising a cleaning step of the substrate whereby the interface between the conductive substrate and metal layer becomes clean.